Bookends, from Sonny Software. It requires Mac OS X 10.2 or later.
Official Description:

    Bookends is a full-featured and cost-effective bibliography, reference, and information management system for students and professionals. With Bookends you can directly search for and import references from many online sources, including the Library of Congress, PubMed, Amazon, and hundreds of libraries from around the world.

Gijs Kessler (International Institute of Social History,
Amsterdam, The Netherlands) wrote the following summary on the H-Mac Discussion Network (a discussion list dealing with the uses of Macintosh computers in the humanities and social sciences):

    With the upgrade to 8, Bookends has the complete set of features
    historians would need. Cite while you write now allows for the correct
    formatting of citations in footnotes, where we would usually place
    them, the number of fields id now elaborate enough to contain all the
    information that historians normally include in their citations and the
    integrated internet search function allows you to search the Library of
    Congress catalogue and transfer references to your database. The only
    thing wanting is output formats for the journals we publish in, but
    that is up to us users to write them, which is really quite easy in
    Bookends. As a start I wrote one for the International Review of Social
    History, which Sonny software was kind enough to include in their
    standard distribution.

Bookends can work with Microsoft Word, Apple Pages, Nisus Writer Express, and Mellel is “Bookends aware” (Mellel/Bookends combination)

Version History
Version 8.1.1 – 9 Aug 2005

    * Flexibility of formatting references for bibliographies has been greatly expanded
    * New sorting options
    * Special title sort
    * More intelligent sorting
    * Database repair function
    * You can copy references from one database to a specific static group in another by drag and drop
    * Insert citation option has been added to the Microsoft Word X/2004 Tools menu and Bookends palette.

Version 8.1 – 8 Jul 2005

    * Substitute dashes for repeated authors – When consecutive references in a bibliography have the same authors, you can have Bookends substitute text (usually a series of emdashes) for the authors’ names.
    * Standardize Names – Global Change -> Standardize Names will cause Bookends to search the Authors and Editors fields for names in surname-last form (that is, without commas, such as John Doe) and change them to surname-first form (e.g. Doe, John).
    * Configurable name display in List View – First author only (default), multiple authors (et al. if more than 2), first…last authors, or all authors.

    * Hide Groups in the List View – A disclosure triangle in the upper left corner of the List View window lets you show/hide the list of Groups.

    * The Live Search field in the List View window has a new appearance
    * Open attachments when in the List View – If an attachment is indicated in the List View, right-clicking (Control-clicking) on it will bring up a contextual menu offering to open it. The new Action pop-up menu will do the same for the first selected reference.

    * E-mail selected references – A right-click (or Control-click) in the reference pane of the List View window will bring up a contextual menu that contains the option E-Mail Selected References. If chosen, Bookends will copy the selected references to the clipboard in the currently active format, launch your e-mail application, and create a new message window containing the reference(s). The references will be in plain text; if you want them in styled text, paste the references from the clipboard into the body of the e-mail.

    * Attachments are opened in the application that created them by default – To display them in a Bookends window, click on the Attach button (or select the attachment from the pop-up menu) with the Shift key held down.

    * Add references to a static group in the List View by drag and drop

    * Info Drawer – Clicking on the Info icon in the List View window opens a drawer that contains either a Concise view of the selected reference or the information in the Notes field. The text is read-only for now.

    * Action pop-up menu – An action icon (gear) in the List View provides the same functions as a right-click in the reference list: e-mail selected references, open attachments belonging to the first selected reference (if ‘indicate attachments’ is selected in Preferences and the selected reference has one), and add the selected references to a static group.

    * Remove references from the Internet Search list – Press Delete or use the Edit -> Clear menu.

    * Better suggestions for attached file names – When attaching a file, the suggested name will vary according to the number of authors/editors (e.g. Smith 2005, Smith & Jones 2005, or Smith et al 2005).

    * Automatically create temporary citations that will be excluded after a scan – This setting in Preferences (Scan & Bibliography tab) will precede temporary citations with the ! character by default.

    * Editing List View preferences does not close open databases

    * Source parsing can be used with MARC records

    * For a Book Chapter, the Title case setting applies to both the chapter and book title

    * Reference navigation menus are enabled when the List View is in front

    * Pressing Command-M in the List View will toggle the first selected reference’s Hit status

    * The minimum database cache size has been increased to 8 MB

    * Place the current date in a reference field with the Insert Date menu option

    * When List View is in front, pressing Option-Command-F places the cursor in the Live Search field

    * When the List View is in front, pressing Command-Shift-O will open the selected reference’s attachments – If the reference does not have any attachments, you will be prompted for a file to attach.

    * When the List View is in front, pressing Command-Shift-U will open your browser and go to the URL in the reference’s URL field.

    * If the Option key is pressed when changing groups in the List View, any text in the Live Search field will be preserved and applied to the newly selected group.

    * Improved import filter tag identification – Import filters that use capital letters at the beginning of a line to define a field will accept numbers as well. This is useful for sources that use RIS output, for example.

    * Bug fixes

    * Fixed: custom citations would sometimes use the wrong form when Ibid. and a secondary order were specified.
    * Fixed: smart searches for a particular reference Type now work.
    * Fixed: unsorted List View windows remain unsorted after an SQL search.
    * Fixed: Quote marks are pruned out more efficiently in certain BibTeX imports.
    * Fixed: a crash that could occur when formatting a reference in which the journal names was > 255 characters long.
    * Fixed: a crash that could occur when importing very large abstracts.
    * Fixed: very long abstracts are no longer truncated.
    * Fixed: scanning text files for citations that contain accented characters works. * Miscellaneous minor bug fixes and many small interface enhancements.

Version 8.0.4 – 19 Apr 2005

    * Fixed: deleting many references at once could cause index corruption or crashes.

    * Fixed: group names can contain the underscore ( _ ) and % characters.

    * Fixed: replacing a static group with another of the same name no longer generates an error message.

    * There is now a popup menu containing the available formats above the formatted reference in the List View window. You can change formats quickly, without having to go to the Biblio -> Default Format -> Format Name menu. This may be useful if you have a preferred format for viewing references (such as one showing the abstract) and another for bibliographies.

    * You can change the text used to indicate “and others” in a format (default is “et al.”).

    * The List View window is updated automatically if you change the marked status of a reference in a Term List.

    * Find In This Reference is enabled when the List View is in front. The search will be performed in the first selected reference, and if a match is found the reference window will be opened and the word highlighted.

    * Search Amazon France and Amazon Canada with Internet Search.

    * Bibliographies sent directly to disk as plain text or BibTeX are converted to MacRoman encoding.

    * BibTeX: changed the representation of some accented characters if they are converted to TeX entities.

    * High resolution Bookends icons now display properly in the Finder.

    * Bookends will offer to move and rename files attached using the Attach button or pop-up menu.

    * Exporting large amounts of data as XML (EndNote 7) is much faster.

    * Hard spaces (Option-space) can be used in a format’s Order field.

    * When formatting references, two or more corporate names (i.e. names ending with a comma) are output with the correct separator between them.

    * Author-date citations will be output correctly even if the author is entered surname-last in the database.

    * The format setting Include Issue # with Vol applies to any reference whose Type contains the word “Journal” or is “Magazine”.

    * You can use a format when it is open in the Format Window.
    * When importing EndNote XML files, names of authors and editors will automatically be converted to surname-first order if necessary.
    * More intelligent handling of punctuation at the end of custom citations and footnotes (e.g. a trailing comma will be replaced with a period, if called for).

    * Minor bug fixes.

Version 8.0.3 – 28 Mar 2005

    * Fixed: a rare case when, under a certain set of certain circumstances, deleting a reference could result in the loss of data from some or all fields in other references.
    * Fixed: journal glossaries stored in the Custom Journal Glossaries folder open correctly when the Utilities -> Journal Glossary -> Edit menu is selected.
    * Fixed: Unicode punctuation (e.g. smart quote marks) in formats are now displayed correctly.
    * Fixed: occasional crashes when attaching files due to bad pathnames stored in Preferences.
    * There are no longer .tmp files associated with open databases.

Version 8.0.2 – 23 Mar 2005

    * Fixed: SQL searches no longer generate an error when they contain the words “ORDER BY”.
    * Fixed: the SortBy command now works with Bookends Server.
    * Fixed: Find/Replace for * (asterisk) no longer causes an assertion error.
    * Fixed: text surrounded by backquotes (`) in formats will be output in the default bibliography font.
    * Fixed: certain Unicode characters (e.g. Å ) lost their accents when copied and pasted into a word processor document.
    * Fixed: large files returned by Bookends Server are no longer truncated.
    * Fixed: drag and drop importing from the Internet Search window when the name of the import filter contains accented characters no longer causes an error message.
    * Fixed: if more than one database is open, selecting it from the Copy To menu in the Internet Search window imports the reference into the selected database.
    * Fixed: a ¬ at the end of a format definition could sometimes cause Bookends to hang when formatting a reference, requiring a force-quit.
    * Fixed: Key fields that are not unique are once again detected and handled as specified in BibTeX Preferences.
    * Fixed: single NOT searches work in Bookends Server.
    * Fixed: the Attachments folder pathname is stored and retrieved correctly even if it contains accented characters.
    * Fixed: consequtive searches would not update the list of hits in the List View window unless you clicked on the Hits group.
    * Fixed: importing from Internet Search with automatic text insertion no longer imports two references, one empty.
    * Fixed: when importing from Internet Search, an ¬ in automatically inserted text is correctly converted to a Return.
    * Custom folders (Formats, Import Filters, and Journal Glossaries) are now stored in ~/Library/Application Support/Bookends/. These folders will be created by Bookends when it is first run. This means that you no longer need to worry about accidentally overwriting any of these files that you have created when upgrading from one version of Bookends to another. If you have created any of these files with Bookends 8.0 or 8.0.1, you should manually move them to this location.
    * The Journal field in the reference window has been enlarged. 18. You can specify that an endash be used to indicate a range of pages in a format. Using ‘p-‘ (dash, or hyphen) to indicate that you want a page range will output whatever is used to separate the page numbers in the reference entry (a dash or an endash). If you use ‘p–’ (endash, made by pressing the Option and the dash (hyphen) key), Bookends will output an endash regardless of whether a dash or endash is actually used in the Pages field of the reference.
    * An endash can be used with Cited Pages. If Bookends encounters a range of pages separated by an endash (e.g. @117–123), it will preserve the endash in the final citation.
    * If you save a strategy for an Internet Search, the corresponding import filter is moved to the Custom Import Filters folder. This prevents you from mistakenly overwriting the modified filter when upgrade to a newer version of Bookends.
    * The Backup menu is enabled when the List View is in front.
    * Change: when using autocomplete, the Return key behaves like the Enter key, accepting the suggested text and moving the cursor to the next line or field.
    * When the List View is opened, the right pane (the list of references) gets the focus.
    * You can scroll to a group in the List View window by typing the first letter(s) of the name.
    * Tabbing between fields is improved when “Turn on full keyboard access” is selected in the Keyboard & Mouse control panel.
    * Incorrect queries sent to Bookends Server are now reported to the client browser and do not require intervention on the server.
    * If “Import to Hits” is enabled, holding down the Shift key when importing references will add the new references to the existing hits, rather than replacing them. Note: when importing by drag and drop, start the drag and then press the Shift key.
    * Bookends Server: now accepts non-Roman characters in searches.
    * Bookends Server: queues concurrent requests more efficiently, and will return an error if access to a database hasn’t been granted within 30 seconds.
    * The Bookends User Guide will be found (via the Help menu) if it is in ~/Documents or in the Bookends Folder.
    * There is an option to separate final citations in a group with just a space.

Version 8.0.1 – 12 Mar 2005

    * Fixed: several bugs in the database engine that could result in crashes or database corruption when importing, copying references between databases by drag and drop, or formatting bibliographies.
    * Fixed: citations created after a Proofreading scan or that are in the author-date form and contain Unicode characters are rendered properly.
    * Fixed: bibliographies are once again sorted properly.
    * Fixed: formats calling for numbered final citations and a sorted bibliography now work properly.
    * Fixed: changes made to the page ranges option in formats are now remembered.
    * Fixed: the last character is no longer lost from Abstract fields containing only a few words.
    * Fixed: HTML output of Unicode (accented and non-Roman) characters is now correct.
    * Fixed: you can create a smart group that searches only for reference Type without getting an SQL error.
    * Fixed: Copy Citation could fail to generate correct citation under certain circumstances.
    * Fixed: trying to use a format that is already open in the Formats Manager now gives the appropriate error message and does not lead to a crash.
    * Fixed: a cosmetic flaw in the display of the unique ID when the toolbar is hidden.
    * Fixed: The “Ignore” field in import filters is no longer ignored.
    * If a date is in “dot notation” (e.g. 01.03.2005), Bookends will use the entire field rather than the year in temporary citations. This ensures that the reference will be found during a scan.
    * Bookends now refuses to import tab-delimited files if they do not match the database design (i.e. were not exported by the Bookends tab-delimited export function).
    * If the citation separator character is present in the Volume field, it is removed when a citation is created.
    * EndNote XML files are now accessible from the Import References dialog even if the Mac file type is not TEXT.
    * In a formatted reference, a question mark at the end of a title will be used even if the format calls for a period.
    * BibTeX importing: A double dash (- -) will be replaced by an en-dash on import. The algorithm to weed out unwanted braces has been improved.
    * BibTeX character conversion: More LaTeX accented character variants are supported. “ and ” are converted to smart left and right quote marks, respectively.